Currently, lithium is being diversely applied to rechargeable battery, glass, ceramic, alloy, lubricant, and pharmaceutical industries. In particular, rechargeable lithium batteries have recently been receiving attention as a main power source for hybrid and electric cars. Further, the market for conventional compact batteries for cell phones and notebooks is expected to continually grow approximately one-hundred times larger.
In addition, lithium has been increasingly applied to electrical, chemical, and energy fields as well as hybrid and electric car industries due to a global movement towards more stringent environmental regulations. Thus, domestic and foreign demand for lithium is expected to be dramatically increased.
Lithium may be obtained from minerals, brine, seawater, and the like as a main source. Although mineral sources such as spodumene, petalite, and lepidolite contain lithium in a relatively large amount ranging from approximately 1 to 1.5%, the lithium is extracted through a complicated process such as floatation, calcination at a high temperature, grinding, acid mixing, extraction, purification, concentration, and precipitation. These processes are cost-ineffective because of high energy consumption and also cause severe environmental pollution due to the use of acids during the lithium extraction.
In addition, approximately 2.5×1011 tons of lithium are reported to be dissolved in seawater, and is extracted by inserting an extraction device containing an absorbent into the seawater, selectively absorbing the lithium, and treating the absorbed lithium with acids. However, since the lithium is contained in a concentration of only 0.17 ppm in seawater, this technology of directly extracting lithium from seawater is extremely inefficient and uneconomical.
Due to the aforementioned disadvantages, lithium is currently extracted from brine produced from natural salt lakes, but salts such as Mg, Ca, B, Na, K, SO4, as well as the lithium are also dissolved in the brine.
Further, lithium is contained in the brine in a concentration ranging from approximately 0.3 to 1.5 g/L, and is usually extracted in a form of lithium carbonate having solubility of about 13 g/L. Even assuming that lithium contained in the brine is completely converted to lithium carbonate, the lithium carbonate is contained in a concentration of 1.59 to 7.95 g/L in the brine (since Li2CO3 has a molecular weight of 74 and Li has an atomic weight of 7, the concentration of lithium carbonate can be estimated by multiplying the concentration of lithium by 5.3 (74÷14≈5.3)). However, since the concentration of the lithium carbonate is mostly lower than its solubility, the extracted lithium carbonate is re-dissolved and thus has an extremely low lithium recovery rate.
Conventionally, in order to extract lithium carbonate from lithium contained in brine, the brine was pumped from a natural salt lake, stored in an evaporation pond, and subsequently naturally evaporated outdoors over a long period of time, for instance, for several months to about one year, to concentrate the lithium by several tenfold. Then, the lithium carbonate was retrieved in an amount greater than or equal to its solubility after precipitating and removing the impurities such as magnesium, calcium, and boron therein.
For instance, Chinese Patent Pub. No. 1,626,443 describes a method of extracting lithium using brine containing concentrated lithium with a low amount of magnesium by evaporating and concentrating the brine under solar heat and repetitively electro-dialysizing it.
However, such a conventional method requires much time for evaporation and concentration of the brine and thus is unproductive, especially during rainy seasons. Further, the loss of lithium is unavoidable, when lithium is extracted along with other impurities in the form of a salt.
In addition, the extracted lithium requires an additional cost and much of energy in order to be converted into a practical form.